Twin electric brush assembly with pressure arm wedge



1964 w. s. KRELLNER 3,158,772

TWIN ELECTRIC BRUSH ASSEMBLY WITH PRESSURE ARM WEDGE Filed Dec. 18, 1962INVENTOR. WALTER aA AsLu/efi- United States Patent PRESSURE ARM WEDGEWalter G. Krellner, St. Marys, Pa., assignor to Stackpole CarbonCompany, St. Marys, Pan, a corporation of Pennsylvania Filed Dec. 18,1962, Ser. No. 245,451 3 Claims. (Cl. 310-246) This invention relates toelectric brushes, and more particularly to a brush formed from a pair ofthin carbon brush ha1f-sections disposed face to face.

It is common practice to make an electric brush for a rotatingelectrical machine from two similar half-sections that are disposed faceto face. The two sections are thin, by which is meant that theirthickness is so small in relation to their length that when they areused with reversible commutators or slip rings they tend to tilt in thebrush holder in a clockwise or counterclockwise direction, dependingupon the direction of rotation of the electrical collector against whichthey ride. Any such change in the position of the brush halves,particularly upon and immediately after reversing the direction ofrotation of the machine, results in new line contacts with the collectorsurface and eventually in so called double Seating. Even though thebrushes do not get into a chattering condition because of the slightleading angle allowed by the necessary clearance in the brush holder,and do not chip or break before the second seat is formed, the newlocation of electrical contact results in a different and less favorabletime of commutation for each direction of rotation, whereby performanceof the machine and the life of the brushes and commutator are impaired.

It is an object of this invention to provide an electric brush of thespilt or two section type, which always engages both sides of the brushholder passage, which does not chatter, regardless of the direction ofrotation of the electrical machine with which the brush is used. Otherobjects are to provide such a brush which can be used with aconventional brush holder without modifying the holder, which is simplein construction, which involves the addition to the brush sections ofonly a single element, and from which that element cannot escape whilethe brush sections are near together.

In accordance with this invention a pair of thin carbon brush halves orsections are disposed side by side and their outer end portions areprovided with a pair of opposed notches. Each notch has end wallsdiverging toward the inner end of the brush and spaced apart by a sidewall that is inclined across the brush section from near its outer facetoward its inner face and end. Together, the notches form a sockethaving side walls converging toward the inner end of the brush andhaving end walls diverging toward said inner end. Disposed in the socketis a wedge that has side walls which slidingly engage the inwardlyconverging side walls of the socket. Consequently, when the wedge ispressed toward the inner end of the brush, it will force the brushsections apart and hold them in engagement with the opposite sides ofthe brush holder passage in which the brush is disposed. The wedge alsohas inwardly diverging end walls adjacent the socket end walls in orderto keep the wedge from accidentally slipping out of the brush socketwhen the wedge-pressing member is removed from the wedge.

The preferred embodiment of the invention is illustrated in theaccompanying drawings, in which FIG. 1 is a view of one end of a brushholder containing my brush, with part of one of the brush sectionsbroken away;

FIG. 2 is a plan view of the brush in the holder taken on the line II-IIof FIG. 1;

FIG. 3 is a cross section of the brush and holder taken on the lineIII-III of FIG. 1;

FIG. 4 is a fragmentary view similar to FIG. 3, but showing thebrush-retaining member held away from the brush and the two sections ofthe brush in engagement with each other;

FIG. 5 is a perspective view of the brush wedge; and

FIG. 6 is a perspective view of a modification.

Referring to FIGS. 1 and 2 of the drawings, a brush holder 1 of suitablewell-known construction is mounted beside a rotating cylindricalelectrical collector 2, such as the commutator or slip ring of arotating electrical machine (not shown). For convenience of descriptiononly, the rotating collector will be referred to herein as a commutator.The machine is reversible so that the commutator can be rotated ineither direction. The brush holder is provided with a rectangularpassage 3 that is disposed radially of the commutator and a shortdistance away from it. Mounted in an opening in the holder outside ofthe brush passage is a spiral spring 4, the outer end of which carriesan insulating pad 5 for pressing a brush B, slidably mounted in thepassage, against the commutator at all times. As is common practice, thebrush is formed from a pair of thin carbon half-sections 7 and 8 thatare disposed face to face. Their outer ends are connected in the usualmanner by shunt wires 9 to a common terminal 10.

It is a feature of this invention that, regardless of the direction inwhich the commutator is rotated, both sections of the brush willcontinually engage the adjoining opposite sides of the brush holderpassage. Accordingly, the outer end portions of the brush sections areprovided with a pair of opposed notches that register with each other toform a socket in the brush. Each notch is threesided; that is, it hasend walls 12 (FIG. 1) that diverge toward the inner end of the brush andwhich are spaced apart by a flat side wall 13 (FIG. 3) that is inclinedacross the brush section from or near its outer face toward or to itsinner face and inner end. Consequently, the socket formed from theseregistering notches has side walls 13 that converge toward the inner endof the brush and it has end walls that diverge toward its inner end.

Disposed in the brush socket is a wedge 14 that has flat side wallswhich lie fiat against the side walls 13 of the socket as shown in FIG.3. The wedge projects from the outer end of the brush and its outersurface preferably is transversely convex. For reasons that will appearlater, it is highly desirable that the wedge be prevented from escapingfrom the socket as long as the two halves of the brush are relativelyclose together. This interlocking of the wedge and the half-sections ofthe brush is accomplished by providing the wedge with end wall-s 15(FIGS. 1 and 5) that diverge inwardly toward the oppo site end of thebrush. These end walls are close to and may be parallel to the end wallsof the socket. The wedge thus is in the shape of an inverted keystonewhen viewed from the side as in FIG. 1, and cannot be removed from theopen side of the socket. To insert the wedge, the half-sections of thebrush have to be separated widely enough to permit the wedge to beinserted upwardly into the two notches, which are then brought togetherto form the socket.

After the wedge has been placed in the brush socket the compact assemblyof the three parts is inserted in the brush holder as shown in FIG. 4,and then the previously retracted spring pad 5 is lowered onto thecurved outer surface of the wedge. The pressure of the spring againstthe wedge will cause it to press the inner end of the brush against thecommutator and simultaneously will cause the wedge to spread the brushhalves apart into engagement with the opposite sides of the holder asshown in FIG. 3. The inclined sides of the wedge are disposed at anangle between about 60 to 120 degrees to each other. A smaller anglewould tend to wedge the brush halves in the holder, while a larger anglewould not spread them apart effectively. An angle of 90 is ideal.

The wedge may be made of various materials, but preferably from anelastomeric material such as rubber or the like in order to provideadditional damping of brush vibrations and to better accommodate itselfto-slight variations in the thickness or length of the brush halves. Thewedge cannot be fastened to either brush section, because that wouldprevent it from sliding against both sections, which is necessary inorder to insure uniform pressure on both brush sections.

It will be seen that with this invention both half-sections of the brushwill always be held against the sides of the bush holder while thecommutator is rotating, regardless of its direction of rotation. As aresult, vibration, chatter, chipping and breakage are greatly reduced oreliminated, the brush seat is not changed with the reversal of thecommutator, the life of the brush and commutator are prolonged, andperformance of the machine remains good. It also will be understood thatconventional brush holders do not have to be altered to receive thisbrush.

When there is such a brush at the bottom of a commutator, considerabledifliculty would be experienced in inspecting the brush or in replacingit if the wedge were free to fall away from the carbon sections when theretaining spring is removed from the brush. This invention insures thatthe wedge will remain in place.

To guarantee that the wedge will not become separated from the brushassembly and lost during shipping or handling of the assembly beforeinsertion in the brush holder, one end of the wedge outside of the brushsocket may be provided with a longitudinally extending ear 17 that has ahole 18 through it, through which loosely extends one of the shunt wires9 that are connected to the carbon sections at the opposite ends of thesocket. Therefore, even though the wedge may come out of the socketwhile the brush is not in use, it will remain with the assembly becauseit cannot leave one of the shunt wires.

A wedge 19 without such an ear is shown in FIG. 6.

I claim:

1. An electric brush assembly adapted to be slidably mounted in a brushholder, comprising a pair of thin carbon brush half-sections disposedside by side and having inner and outer side faces and inner and outerends, the outer end portions of said sections being provided with a pairof opposed notches each having end walls diverging toward the inner endof the brush and spaced apart by a side wall inclined across the brushsection from near its outer face toward its inner face and end, saidnotches to gether forming a socket having side walls converging towardthe inner end of the brush and having end walls diverging toward saidinner end, and a wedge in said socket having side walls slidinglyengaging said socket side walls, whereby when the wedge is pushed towardthe inner end of the brush it will force said sections apart, and saidwedge having inwardly diverging end walls adjacent said socket end wallsto keep the wedge from accidentally slipping out of the socket.

2. An electric brush assembly according to claim 1, in which the wedgeis made of elastorneric material.

3. An electric brush assembly adapted to be slidably mounted in a brushholder, comprising a pair of thin carbon brush half-sections disposedside by side and having inner and outer side faces and inner and outerends, shunt wires projecting from the outer ends of said sections, theouter end portions of said sections being provided with a pair ofopposed notches each having end walls diverging toward the inner end ofthe brush and spaced apart by a side wall inclined across the brushsection from near its outer face toward its inner face and end, saidnotches together forming a socket having side walls converging towardthe inner end of the brush and having end walls diverging toward saidinner end, and a wedge in said socket having side walls slidinglyengaging said socket side walls, whereby when the wedge is pushed towardthe inner end of the brush it will force said sections apart, and saidwedge having inwardly diverging end walls adjacent said socket end wallsto keep the wedge from accidentally slipping out of the socket, and saidwedge being provided at one end with an car outside of said socket, theear being provided with a hole loosely receiving one of said shunt wiresto attach the wedge to that wire.

References Cited in the file of this patent UNITED STATES PATENTS2,488,788 Weilbaecher Nov. 22, 1949 2,796,544 Silverman June 18, 1957FOREIGN PATENTS 971,394 Germany Jan. 22, 1959 1,020,066 France Nov. 12,1952

1. AN ELECTRIC BRUSH ASSEMBLY ADAPTED TO BE SLIDABLY MOUNTED IN A BRUSHHOLDER, COMPRISING A PAIR OF THIN CARBON BRUSH HALF-SECTIONS DISPOSEDSIDE BY SIDE AND HAVING INNER AND OUTER SIDE FACES AND INNER AND OUTERENDS, THE OUTER END PORTIONS OF SAID SECTIONS BEING PROVIDED WITH A PAIROF OPPOSED NOTCHES EACH HAVING END WALLS DIVERGING TOWARD THE INNER ENDOF THE BRUSH AND SPACED APART BY A SIDE WALL INCLINED ACROSS THE BRUSHSECTION FROM NEAR ITS OUTER FACE TOWARD ITS INNER FACE AND END, SAIDNOTCHES TOGETHER FORMING A SOCKET HAVING SIDE WALLS CONVERGING TOWARDTHE INNER END OF THE BRUSH AND HAVING END WALLS DIVERGING TOWARD SAIDINNER END, AND A WEDGE IN SAID SOCKET HAVING SIDE WALLS SLIDINGLYENGAGING SAID SOCKET SIDE WALLS, WHEREBY WHEN THE WEDGE IS PUSHED TOWARDTHE INNER END OF THE BRUSH IT WILL FORCE SAID SECTIONS APART, AND SAIDWEDGE HAVING INWARDLY DIVERGING END WALLS ADJACENT SAID SOCKET END WALLSTO KEEP THE WEDGE FROM ACCIDENTALLY SLIPPING OUT OF THE SOCKET.